Piston: Service and Repair
11 25 530 Removing and installing or replacing all pistons (N18)Special tools required:
Warning!
Safety goggles must be worn when performing repair work on the gudgeon pin circlip.
Important!
If pistons, connecting rods and bearing shells are reused, they must be reinstalled in the same places.
Connecting rods and connecting rod bearing caps are denoted with the same pairing letters; mixing them up will result in engine damage.
Piston and gudgeon pins are paired and must not be fitted individually.
Necessary preliminary work:
^ Remove engine.
^ Mount engine on assembly stand.
^ Remove intake plenum.
^ Remove cylinder head.
^ Remove oil sump.
^ Remove oil pump.
Note:
In event of heavy oil carbon residue:
Carefully remove oil carbon residue from cylinder wall.
Note:
Graphic shows N46.
Note:
Mark all pistons and connecting rods with a pen prior to removal.
Example:
Direction of arrow (1) points to camshaft drive.
Cylinder allocation (2) per cylinder.
Note:
Mark all pistons and connecting rods with a pen prior to removal.
Example:
Mark cylinder allocation (1) per cylinder.
Direction of arrow (2) points to camshaft drive.
Release connecting rod bolts (1).
Tightening torque, 11 24 1AZ.
Remove connecting rod bearing cap.
Important!
Connecting rods and connecting rod bearing caps are denoted with the same pairing letters; mixing them up will result in engine damage.
Important!
Risk of damage! to oil spray nozzle.
11 9 620 Attach special tool in connecting rod.
Press out connecting rod and piston to cylinder head side.
Warning!
Safety goggles must be worn for the next operation.
Warning!
Safety goggles must be worn.
Important!
Piston and gudgeon pins are paired and must not be fitted individually.
Lever out gudgeon pin circlip with a screwdriver in direction of arrow.
If necessary, replace connecting rods.
Installation note:
The gudgeon pin must be able to be pressed through the bush by hand with little force and must not display any significant play.
Measure piston installation clearance:
Measure piston diameter with micrometre at measuring point A from lower edge of piston and offset by 90° to piston pin axis.
Piston diameter at measuring point A.
Adjust micrometre to cylinder bore of engine block. Set internal measuring device on micrometre to zero. Measure bottom, centre and top of cylinder bore in direction of travel and direction of engine rotation.
Diameter of cylinder bore.
Piston installation clearance.
Total permissible wear clearance.
If necessary, replace piston.
Install all piston rings.
Install all bearing shells.
Oil piston and piston rings.
11 9 670 Pre-install piston in special tool.
Screw special tool 11 9 620 into connecting rod.
Installation note:
11 9 620 Check protective lugs on special tool for correct position and damage.
Insert piston with connecting rod in cylinder.
Important!
Risk of breakage of piston rings.
Press in piston with finger pressure only, do not drive in (see arrows).
Insert piston (1) so that arrow on piston crown points to camshaft drive.
If reusing the pistons, assign cylinder allocation (2) to correct cylinder.
Press in piston with special tool 11 9 670.
Important!
Point of fracture (1) on connecting rod.
Conrod and connecting rod bearing cap are identified with pairing letters (2) and must not be mixed up.
Mixing them up or incorrect assembly of the connecting rod bearing cap on the connecting rod will result in engine damage.
Both pairing letters (2) must be together on one side.
Apply a light coat of oil to crankshaft journals.
Attach connecting rod to crankshaft journal.
Remove special tool 11 9 620.
Fit bearing caps (2) so that pairing letters match up.
Check cylinder identification markings (1).
Direction of arrow (2) points to camshaft drive.
Install new connecting rod bolts (1).
00 9 120 Carry out torsion angle adjustment of connecting rods with special tool.
Tightening torque: 11 24 1AZ
Assemble engine.
